1. Field of the Invention
This invention generally relates to the management of resources in a data processing system and more particularly to the management of a disk array storage device.
2. Description of Related Art
Many data processing systems now incorporate disk array storage devices. Each of these devices comprises a plurality of physical disks arranged into logical volumes. Data on these devices is accessible through various control input/output programs in response to commands, particularly reading and writing commands from one or more host processors. A Symmetrix 5500 series integrated cached disk array that is commercially available from the assignee of this invention is one example of such a disk array storage device. This particular array comprises multiple physical disk storage devices or drives with the capability of storing large amounts of data up to one terabyte or more. The management of such resources becomes very important because the ineffective utilization of the capabilities of such an array can affect overall data processing system performance significantly.
Generally a system administrator will, upon initialization of a direct access storage device, determine certain characteristics of the data sets to be stored. These characteristics include the data set size, and volume names and, in some systems, the correspondence between a logical volume and a particular host processor in a multiple host processor system. Then the system administrator uses this information to configure the disk array storage device by distributing various data sets across different physical devices accordingly with an expectation of avoiding concurrent use of a physical device by multiple applications. Often times allocations based upon this limited information are or become inappropriate. When this occurs, the original configuration can degrade overall data processing system performance dramatically.
One approach to overcoming this problem has been to propose an analysis of the operation of the disk array storage device prior to loading a particular data set and then determining an appropriate location for that data set. For example, U.S. Pat. No. 4,633,387 to Hartung et al. discloses load balancing in a multi-unit data processing system in which a host operates with multiple disk storage units through plural storage directors. In accordance with this approach a least busy storage director requests work to be done from a busier storage director. The busier storage director, as a work sending unit, supplies work to the work requesting, or least busy, storage director.
U.S. Pat. No. 5,239,649 to McBride et al. discloses a system for balancing the load on channel paths during long running applications. In accordance with the load balancing scheme, a selection of volumes is first made from those having affinity to the calling host. The load across the respective connected channel paths is also calculated. The calculation is weighted to account for different magnitudes of load resulting from different applications and to prefer the selection of volumes connected to the fewest unused channel paths. An optimal volume is selected as the next volume to be processed. The monitored load on each channel path is then updated to include the load associated with the newly selected volume, assuming that the load associated with processing the volume is distributed evenly across the respective connected channel paths. The selection of the following volume is then based on the updated load information. The method continues quickly during subsequent selection of the remaining volumes for processing.
In another approach, U.S. Pat. No. 3,702,006 to Page discloses load balancing in a data processing system capable of multi-tasking. A count is made of the number of times each I/O device is accessed by each task over a time interval between successive allocation routines. During each allocation, an analysis is made using the count and time interval to estimate the utilization of each device due to the current tasks. An estimate is also made with the anticipated utilization due to the task undergoing allocation. The estimated current and anticipated utilization are then considered and used as a basis for attempting to allocate the data sets to the least utilized I/O devices so as to achieve balanced I/O activity.
Each of the foregoing references discloses a system in which load balancing is achieved by selecting a specific location for an individual data set based upon express or inferred knowledge about the data set. An individual data set remains on a given physical disk unless manually reconfigured. None of these systems suggests the implementation of load balancing by the dynamic reallocation or configuration of existing data sets within the disk array storage system.
Another load balancing approach involves a division of reading operations among different physical disk drives that are redundant. Redundancy has become a major factor in the implementation of various storage systems that must also be considered in configuring a storage system. U.S. patent application Ser. No. 08/653,154 filed May 24, 1996 (now U.S. Pat. No. 5,819,310 granted Oct. 6, 1998) discloses such a redundant storage system with a disclosed disk array storage device that includes two device controllers and related disk drives for storing mirrored data. Each of the disk drives is divided into logical volumes. Each device controller can effect different reading processes and includes a correspondence table that establishes the reading process to be used in retrieving data from the corresponding disk drive. Each disk controller responds to a read command that identifies the logical volume by using the correspondence table to select the appropriate reading process and by transferring data from the appropriate physical storage volume containing the designated logical volume.
Consequently, when this mirroring system is implemented, reading operations involving a single logical volume do not necessarily occur from a single physical device. Rather read commands to different portions of a particular logical volume may be directed to any one of the mirrors for reading from preselected tracks in the logical volume. Allowing such operations can provide limited load balancing and can reduce seek times.
Other redundancy techniques and striping techniques can tend to spread the load over multiple physical drives by dividing a logical volume into sub-volumes that are stored on individual physical drives in blocks of contiguous storage locations. However, if the physical drives have multiple logical volumes, sub-volumes or other forms of blocks of contiguous storage locations, the net effect may not balance the load with respect to the totality of the physical disk drives. Thus, none of the foregoing references discloses or suggests a method for providing a dynamic reallocation of physical address space based upon actual usage.
Once a pair of logical volumes have been selected for dynamic reallocation, an exchange, or swap, can occur by selecting an unused area in one of the physical disk drives to operate as a buffer. This may be an unused area in a physical disk storage device or in a dynamic spare physical disk storage device. The general use of physical disk storage devices as dynamic spares is known in the art. In other circumstances it may be possible to utilize a cache memory, such as the cache memory 33 in FIG. 2, as a buffer. If a single buffer is to be used, a concurrent copy or other transfer sequence can move (1) a first logical volume from a first physical disk storage device to the buffer, (2) the second logical volume to the corresponding area in the first physical disk storage device and (3) the logical volume buffer to the area in the second physical disk storage device that had contained the second logical volume. Although a concurrent copy or other analogous procedure may enable the exchange to occur on-line, unacceptable performance degradation for the duration of the transfer can occur.
As described in previously identified U.S. Pat. No. 6,237,063, logical volumes acting as BCV devices, as described in the foregoing U.S. Pat. No. 6,088,766, might be adapted for performing such an exchange. For example, assuming that the first and second logical volumes are selected, the exchange process initially could transfer the data from the first and second logical volumes to the first and second BCV logical volumes, respectively. After recognizing the first and second logical volumes, the exchange would be completed by transferring the contents of the second BCV logical volume 92 to new second, i.e., the old first, logical volume and by transferring the contents of the BCV logical volume to the new first, i.e., the old second, logical volume.
This approach utilization of BCV logical volumes and the basic commands associated with such devices can require additional operations. Consequently in certain applications it is possible to produce significant delays in the normal operating procedures such that the transfer does not occur transparently to any user or application software. Moreover as conventional BCV commands do not readily lend themselves certain transfers required for an exchange, the process for making the exchange becomes cumbersome.
Therefore it is an object of this invention to provide a dynamic reallocation of a disk array storage device to reduce any imbalance of load requirements on each physical disk storage device.
Another object is to provide a method for dynamically reallocating logical volumes on physical disk storage devices transparently to the normal operation of such physical disk stroage devices and logical volumes with user or application software.
Yet another object of this invention is to provide a dynamic reallocation of logical volumes in a disk array storage device that utilizes a simple process.
Yet still another object of this invention is to provide for a dynamic reallocation of logical volumes in a disk array storage device without any loss of preexisting redundancy for the logical volumes during the transfer.
In accordance with one aspect of this invention, data in two logical volumes, having first and second data processing identifications, respectively, is exchanged by establishing data transfer paths between the first and second logical volumes and third and fourth logical volumes, respectively. Then the data in the first and second logical volumes is copied to the third and fourth logical volumes, respectively, independently of and concurrently with user or application generated responses to I/O requests to the first and second logical volumes. Next the first and second logical volumes are reconfigured to have the second and first data processing identifications, respectively. Thereafter the data in the third and fourth logical volumes transfers to the second and first logical volumes, respectively.
In accordance with another aspect of this invention, data in a first logical volume, that is a mirror in a first set of mirrored logical volumes, is exchanged with data stored in a second logical volume that is a mirror in a second set of mirrored logical volumes. The method includes the steps of establishing data transfer paths between the first and second logical volumes and third and fourth logical volumes, respectively and then copying the data in the first and second logical volumes to the third and fourth logical volumes, respectively, independently of and concurrently with responses to user or application generated I/O requests to the first and second logical volumes. Upon completion of the copying, the first and second logical volumes are configured to be mirrors in the second and first sets of mirrored logical volumes, respectively; and then the data in the third and fourth logical volumes is transferred to the second and first logical volumes.